Fw: Re: Surging and erratic boost update

rguzz at mindspring.com rguzz at mindspring.com
Sat Jan 6 19:46:32 EST 2007

Mike's pressure tester revealed no  leaks...car will pick up to full boost at WOT (16psi), oscillate, then drop steadily down to 9psi repeatedly. Surging is intermittent and worse when engine is cold.
New 02 sensor, plugs, bpv, wires should be okay. Will check codes next week when I review how to do this.
Will go back to SJM's check list to trouble shoot low boost. But the list is a bit daunting and discouragingly lengthy.
Any simple next steps?
Thanks again.

-----Forwarded Message-----
>From: Phil and Judy Rose <pjrose at frontiernet.net>
>Sent: Dec 31, 2006 1:16 PM
>To: rguzz at mindspring.com
>Cc: 200q20v at audifans.com
>Subject: Re: Surging and erratic boost
>At 11:56 AM -0500 12/31/06, rguzz at mindspring.com wrote:
>>186k miles 200tq TAP chipset (yeah I know) there is a worsening 
>>surge intermittently beginning at around 2.5-3k rpm. The external 
>>boost gauge as I run the car a bit hard will hover at 16 psi, 
>>sometimes very steady other times wildly
>>I'd like to clean, check function of all sensors (hall, etc) but I 
>>sort of think these function on an all or nothing basis.
>>Could this be as simple as a boost leak? I don't hear one and power 
>>seems good. Should I replace the WGFV on a trial and error basis? 
>>Where else should I look?
>>Thanks for your input.
>When I hear "surge" complaints, I tend to suspect the oxygen sensor. 
>Does the surge seem most pronounced while at steady throttle? How old 
>is that sensor? Likely to be bad if more than 4 or 5 yrs old.
>I think that achieving 16 psi on an external gauge indicates that the 
>WGFV is unlikely to have failed completely (absolute WGFV "failure" 
>results in a limit of about 0.4 bar boost, i.e., about 6 psi) 
>although I suppose the valve could simply be erratic or sluggish.
>As to your boost gauge behavior: how much boost deviation (+/-) do 
>you see when your gauge is "wildly" varying? My own (Lehmann-chipped) 
>200 has always had a fluttering boost gauge needle when it reaches 
>the boost limit of about 18 psi. At that instant the needle flutters 
>rapidly at about +/- 1 psi (seen with a new wgfv), but I have no 
>leaks, no surges, and good fuel mileage, so I've decided that this 
>behavior is "normal", at least for my "el cheapo" gauge. But in 
>contrast to what you describe, at the point when true boost limit is 
>reached in my car, the gauge needle always flutters and is _never_ 
>steady. I imagine that if my car was failing to achieve true maximum 
>boost from time-to-time, then the gauge might behave like yours does.
>I recommend you check more carefully for a pressure leak; set up a 
>careful pressure test of your intake manifold and you may be 
>surprised at what you find.
>*  Phil & Judy Rose           Rochester, NY  *      
>*        mailto:pjrose at frontiernet.net       *

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